The present invention relates to a piston ring for use in an internal combustion engine, and more particularly, to a type thereof capable of being employed in the internal combustion engine which uses high lead content fuel or which is exposed to corrosive atmosphere.
At present, while employment of non lead or lead free fuel has been progressing in light of the problem of public pollution, the employment of an internal combustion engine which uses high lead content fuel is also available throughout the world. In the internal combustion engine employing high lead content fuel, in order to avoid excessive wear, thick chromium plating is provided onto an outer peripheral surface of the ring so as to sustain extensively corrosive atmosphere such as HCl atmosphere.
However, sufficient effect has not been obtainable in light of productivity and cost.
On the other hand, a piston ring whose sliding portion is subjected to nitriding treatment has been developed. However, excessive wear such as scuffing may occur in accordance with specific operating condition of the engine. U.S. Pat. No. 4,407,515, commonly assigned, discloses a combined oil ring in which spacer expander and side rails are subjected to low temperature gas nitriding treatment. Further, co-pending U.S. application Ser. No. 571,630 discloses a piston ring having a ring body made of cast iron or steel having its entire surface provided with a soft-nitride layer, and outer peripheral surface provided with a spraying layer.